When four people with a combined mass of 320 kg sit down in a car, they find that the car drops .80 cm lower on its springs. THen they get out of the car and bounce it up and down. What is the frequency of the car's vibration if its mass (empty) is 2.0 X 10^3 kg?

The spring constant is k = (2000+320)*g/(deflection)
2000 is the mass of the car, and 320 the mass of the occupants.

The frequency of vibration of the empty car is
f = (1/ 2 pi) sqrt (k/2000)